(1) Field of the Invention
The present invention relates to a stacked type solid electrolytic capacitor, and more particularly to such a capacitor constituted by a plurality of stacked single plate capacitors each having a dielectric oxide film, a solid electrolytic film and a negative electrode member laminated on a surface of a predetermined region of a positive electrode member formed by a film-forming metal such as aluminum or tantalum having a valve action characteristic.
(2) Description of the Related Art
A conventional solid electrolytic capacitor uses a structure in which a dielectric oxide film is formed on a foil surface of a film-forming metal such as aluminum or tantalum having a valve action characteristic. On this dielectric oxide film, there is provided as solid or static electrolyte an inorganic semiconductor film of such as manganese oxide (MnO.sub.2) and lead oxide (PbO.sub.2), charge transfer complex such as tetracyanoquinodimethane complex, or conducting polymer such as polypyrrole and polyaniline.
In recent years, there have been demands for electric and electronic devices to be miniaturized by using smaller electronic components, while at the same time keeping or increasing electric performance, i.e., desired capacitance (microfarad of capacitance). Also, as surface mounted designs become more common, so the need for chip type electrolytic capacitors becomes greater.
In view of the above demands and needs, there have been proposed (in Japanese Patent Application Kokai Nos. 3-21006 (A) and 3-116813 (A)) electrolytic capacitors in which a foil is synthetically formed by, for example, aluminum etching, on the surface of which a dielectric oxide film is formed, with a conductive polymerized film being formed on the dielectric oxide film, thereby providing a sheet type capacitor. The electrolytic capacitor proposed can be a wound sheet type to give a wound electrolytic capacitor or can be sealed in metal case to give a sealed electrolytic capacitor. There has also been proposed (in Japanese Patent Application Kokai No. 3-145115 (A)) a laminated type solid electrolytic capacitor in which a plurality of capacitor elements (single plate capacitors) are laminated, with positive electrode sections of these capacitor elements being subjected to cold-pressure, so that the portions being pressed can be welded by laser.
FIGS. 1A and 1B show a cross-sectional view and a top view respectively of an example of the conventional stacked type solid electrolytic capacitor referred to above.
The conventional stacked type solid electrolytic capacitor shown is constituted by a plurality (four in the example) of single plate capacitors 21 stacked on top of each other, wherein the negative electrode sections are electrically and mechanically interconnected by silver paste element 23. Also, the positive electrode sections 25 extending out from the sides of the bodies of the plate capacitors are pressed together by cold-pressure process and are then laser-welded, so that the positive electrode sections 25 are mechanically and electrically interconnected at the welded portions 26.
However, in the conventional electrolytic capacitor described above, there are problems in that the curved or bent portions of the metal foils are susceptible to mechanical stresses thereby causing the deterioration of the electrical characteristics of the capacitor. Also, the gaps which unavoidably exist between the metal foils makes size reduction difficult in the fabricated capacitor.
Also, in the stacked type solid electrolytic capacitor shown in FIGS. 1A and 1B, since the positive electrode sections 25 extending out from the body portion of the plate capacitor 21 need to be Joined together by a cold-pressure process, it is necessary for the positive electrode sections 25 to be made long in the direction in which they extend out. This makes size reduction difficult and also, since the base portions of the positive electrode sections are bent when they are pressed together, the metal foils of the bent portions are susceptible to mechanical stresses thereby causing the deterioration of electrical characteristics. Also, when the positive electrode sections 25 are laser-welded, it is difficult to have a plurality of metal foils thoroughly welded simultaneously.